Transformer having novel multiple winding and support structure and method of making same

ABSTRACT

Electrical apparatus includes electrical coil means formed of multiple turns of enamel-covered electrical wire axially mounted on a core of magnetic material in electromagnetic energy coupling relationship therewith, and a relatively flat flexible electrical cable containing a plurality of spaced parallel conductors extending between the cable ends contains a loop shaped portion extending about an axis of said core over an arcuate distance greater than 180 degrees. The method of adding a plurality of electrical windings to an electrical transformer of the type containing electrical coil means having a primary winding and at least one secondary winding, with said coil means having a central axis and a central passage coaxial with said axis; a core of magnetic material with said core having a portion extending through said central passage to support said coil means thereon, includes the step of forming into a loop extending about the axis of said coil an elongated flat cable of the type containing a plurality of spaced parallel electrical conductors insulated from one another.

BACKGROUND OF THE INVENTION

The present invention relates to electrical transformers and, moreparticularly, my invention relates to inverter type ferrite coretransformers of the type containing a plurality of fractional or singleturn secondary windings, to the method of manufacturing such windingsand to supporting the transformer in the combination of an electricaldevice.

The transformer is a known electrical component which contains at leasttwo electrical windings formed into a coil or coils mounted on a core ofmagnetic material by means of which AC electrical energy is coupled fromone winding to the other, respectively termed the "primary" and the"secondary". Generally each of those windings are formed of a largenumber of turns of electrical enamel coated wire fabricated in the formof a coil by means of conventional coil-winding machinery. Thereafter inthe assembly of the transformer the formed coil is mounted to the coreof magnetic material. Generally, the voltage relationship between theprimary winding and the secondary winding or windings is governed ingreat part by the "turns ratio"; the ratio of turns in a secondary tothe turns of the primary. Where the ratio is greater than one a"step-up" voltage relationship exists and where less than one, a"step-down" relationship exists. By design a transformer may contain oneor the other or both step-up and step-down windings. Each of these priorart structures permit of many variations and methods of manufacturewhich are widely known in the industry and in the patent literature, towhich the reader may make reference. By way of further background it isrecalled by those skilled in this art that manufacture of electricalcoils for transformer application involves winding of the coil oncoil-winding machinery, using typically enamel coated wire, and involvesset-up procedures requiring time and labor. In many transformer coilsthe beginning, tap and end turns of the enamel coated wire windings areconnected to separate electrical insulated jacketed leads respectively,to form the circuit connections by means of which the transformerwindings are connected electrically to other circuits. In otherstructures the end leads may be connected to electrical terminals builtinto coil bobbins used in connection with some transformers of moreexpensive structure so that the transformer may be easily "plugged-in"to a printed circuit board. In one type of electronic device, namely asolid state inverter-oscillator type circuit, for operating one or moregaseous discharge devices, such as a fluorescent lamp of the rapid starttype, circuitry is included for converting either low voltage DC or ACline voltage of low frequency, typically 60 hertz, to the high-voltagehigh-frequency energy supplied to the lamp, as well as to providelow-voltage current to the lamp's heaters. This electronic deviceincludes a transformer containing a primary winding and a plurality ofsecondary windings which are located on a core of magnetic material,such as the conventional ferrite core material useful at highfrequencies or magnetic steel laminations formed into a transformercore. Although a high-voltage secondary winding is required containing alarge number of turns of enamel coated wire efficiently assembled byhigh speed coil winding machinery, other secondary windings intended inthe apparatus to provide the heater currents at low voltage to thefluorescent lamp cathodes, require only one or two turns at most. In thecase of a solid state ballast intended to operate two rapid-start typelamps, for example, there is a requirement for three such low voltageheater windings consisting of a single wire turn, at least oneadditional low voltage winding for which a single wire turn suppliessatisfactory voltage, and a further secondary winding intended to supplyelectrical components within the device requiring only two turns ofwire. In other applications a fractional turn winding of 1/2 turn or 3/2turns is all that is required. As the reader familiar with the methodsof transformers manufacture can appreciate, to accomplish windingmanufacture according to the one existing procedure would require thewinding and insulation of a plurality of single turns of wire which, ifenamel wire were used, may require the attachment of electrical jacketedleads, as described above, or to alternatively wind the individual oneturn windings with insulation jacketed wire. Obviously a certain amountof time and effort is involved in handling a number of these low voltagesecondary windings and this time and effort accordingly is equated withunnecessary expense in manufacture and is necessarily reflected in theprice of the product. A higher price for a product in turn acts to limitits marketability, even though the product is technically innovative andpossesses attractive advantages, if the cost of obtaining thoseadvantages is too great in comparison to conventional or old methods ofobtaining the essential functions performed by the product.Specifically, by way of example, the solid state type of fluorescentlamp ballast possesses many advantages over the conventionalelectromagnetic type for which it may serve as a substitute. The presentcost of such solid state ballast, however, is one factor that hasheretofore limited marketability since in the minds of many potentialbuyers the additional cost exceeds the additional benefits from suchsubstitution.

My invention simplifies the winding structure and assembly oftransformers having some secondary windings containing but a fractionalor small number of turns and thereby reduces the cost of manufacture ofsolid state inverter type ballast incorporating a transformer, and, moreparticularly, reduces the cost of manufacture of the transformer as amajor advantage. A related object is to provide a transformer containinga plurality of single turn windings and a method of manufacturing samewithout the necessity of separately handling individual turns. A stillfurther aspect of the invention is to provide a transformer windingstructure which assists in supporting the transformer upon a printedcircuit board.

SUMMARY OF THE INVENTION

Briefly, my invention in a transformer, includes a core of magneticmaterial; electrical coil means containing a plurality of turns ofenamel covered electrical wire formed about an axis, said coil meansmounted axially on said core; a flat electrically insulated cablecontaining a plurality of spaced apart parallelly extending conductors,said cable having a loop shaped portion extending about the periphery ofsaid coil means, said loop shaped portion extending an arcuate distancegreater than 180 degrees about the axis of said coil, and said cablecontaining first and second ends.

Commencing with a transformer structure containing an iron core havingan electrical coil mounted thereon in electromagnetic energy couplingrelationship therewith, a plurality of single turn secondary windings isformed by the step of threading or looping, as variously termed, aboutthe outer periphery of the electrical coil a flat cable containing aplurality of spaced electrical conductors. Further, in accordance withthe method of my invention, an electrical printed circuit board isprovided containing electrical terminals adapted to mate with theconductors of the aforedescribed cable.

A printed conductor on the circuit board extends between one terminal ofthe group of terminals intended to be attached to one end of said cableto a terminal of the second group of terminals intended to be connectedto the remaining end of said flat cable to thereby define in combinationwith a conductor in said cable a portion of a winding turn on saidcircuit board with the step of connecting each end of the cable to thecorresponding terminals on said circuit board serving to complete asecondary winding and to form a strap-like arrangement to provide aholding force for holding the transformer at least temporarily inposition on said circuit.

The foregoing objects and advantages of my invention together with thestructure and steps characteristic thereof, as well as additionaladvantages and equivalent elements, are better understood by consideringthe preferred embodiments of the invention described in the detaileddescription which follows hereinafter in this specification inconnection with the illustrations thereof presented in the drawings.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings:

FIG. 1 illustrates an embodiment of the invention in exploded view;

FIG. 2 is an end view of the embodiment of FIG. 1 in assembled relation;

FIG. 3 is an end section view of the embodiment of FIG. 1 installed in acontainer;

FIG. 4 is an electrical schematic of the transformer of FIG. 1;

FIG. 5 is an end view of an alternate embodiment of my invention;

FIG. 6 partially illustrates in different scale a portion of a circuitboard useful in the combination of FIG. 1 and the relationship betweenprinted circuit board conductors and the conductors of the ribbon-likecable therein;

FIG. 7 is a partial illustration of a portion of another circuit boarduseful in the combination of FIG. 1 to form a two-turn secondarywinding;

FIG. 8 illustrates in end view an embodiment of the invention containingone-half turn secondary windings;

FIG. 9 illustrates in end view another embodiment, the structure ofwhich includes two ribbon-like cables, each of which forms half-turnsecondary windings;

FIG. 10 is an end view of a further embodiment of a transformercontaining a plurality of one-half turn secondary windings;

FIG. 11 is an end view of an alternate embodiment related to theembodiments of FIGS. 9 and 10;

FIG. 12 illustrates in end view a still further embodiment of theinvention containing a plurality of one-half turn secondary windings;and

FIG. 13 is an end view of still another embodiment of the invention, thestructure of which includes a plurality of single-turn and a pluralityof one-half turn secondary windings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is made to the embodiment presented in FIG. 1 in which thetransformer, including core 1 of magnetic material, is illustrated inexploded relationship to a printed circuit board 3 which underlies thecore. The magnetic core, suitably of magnetic material such as ferrite,possesses an "E-I" configuration known in the art, defining a center legupon which an electrical coil 5 is mounted and two opposed outer legswhich extend parallel to the center leg, and defining in the spacebetween the described parallel legs two core windows in which coil 5 isreceived. Electrical coil 5 is of any conventional electrical coilstructure configured into a cylindrical or rectangular shape having acentral axial passage and containing a primary winding to which start 7,finish 9 and center tap 11 leads are attached and an overlying multiturnhigh voltage secondary winding to which leads 13, 15 and 17 are attachedas the start, finish and center tap. The coil is inserted onto thecenter core leg which extends through the coil's central passage. It isnoted that although the aforedescribed windings are described as beingin overlying relationship, it is clearly within the scope of the presentinvention, as becomes apparent, for these two windings to be formed asseparate coils arranged in a side-by-side relationship. As is depictedin FIG. 1, some clearance is provided between the periphery of coil 5and the outer core legs. A relatively flat cable 21 is threaded orinserted through the clearance between coil 5 and one outer core leg onone side and loops around or girdles the underside of the coil, notvisible in this figure, extends through the remaining clearance betweenthe coil and the remaining outer leg. Connectors 23 and 25 containingsuitable electrical terminals are attached to a respective end of thiscable. As is there shown, the cable is then wrapped around the outercore legs as well as the coil, much like a strap. As is furtherdepicted, cable 21 is seen to contain six parallely extending conductorsin spaced relationship electrically insulated from one another as partof a thin flexible plastic-like carrier that is flat, having a widthmany times greater than its thickness so as to be ribbon-like inappearance. These kinds of flat cables are well known in the art; onetype is available as a plurality of separate jacketed wires with jacketsfused together in a layer which appear to be the cable product soldunder the trade name "Scotchflex" by the 3M Company, and another type isknown as a ribbon cable, in which flat conductors are formed within aflat plastic matrix. These cables have generally been used to provideflexible electrical interconnections in applications requiring largenumbers of interconnections, typically in computer or data processingapparatus. Circuit board 3 underlying the transformer includes a groupof six spaced electrical socket openings or terminals, generallyrepresented at 27, with which to form mating electrical interconnectionwith the protruding terminals of cable connector 25 and these may besoldered together in place. Similarly, the left side of the circuitboard is a second group of six spaced socket openings or terminalsgenerally represented as 29 into which the extending prongs, not visiblein the figure, of connector 23 attached to the left end of cable 21 maybe inserted and soldered to form an electrical and mechanical connectiontherewith.

As so joined together, a firm mechanical bond is created between thecable ends and the circuit board. Inasmuch as the cable is strappedabout the outer legs of transformer 1, such strapping serves as arestraint to hold the transformer in place upon the circuit board. Inaddition, inasmuch as each of the conductors within the cable extendsarcuately at least half-way or 180 degrees around the center core leg, acorresponding plurality of one-turn windings, so to speak, is formed.

The circuit board of a typical electronic apparatus, such as a solidstate ballast, contains a plurality of other electrical componentsincluding transistors, capacitors, resistors, generally represented at31, the exact details of which are not necessary to the understanding ofthe invention but which are partially illustrated in figure simply forcompleteness. Likewise, electrical conductors extend on the uppersurface as shown, or, alternatively, along the underside of the boardfrom each of the contacts in the group 27 and 29 to suitable locationswithin the electronic circuit 31. Attention is drawn to conductor 28 onthe circuit board which extends from the first terminal in group ofterminals 27 to the second terminal in group of terminals 29. With thecable connected in place to the corresponding terminals, an electricalcircuit or path is formed which extends from the first terminal in group29 through the cable and one turn part way around the periphery of coil5 to the first terminal in group 27, and from that location extendsthrough conductor 28 to the second terminal of the left hand group ofterminals, and extends further through the second adjacent conductor incable 21 and again part way around the coil periphery and core to thesecond terminal in the terminal group 27. The defined electrical paththus extends twice around the core of the transformer to thereby form a"two-turn" secondary winding. By contrast, each of the other definedelectrical paths illustrated simply extend about the coil and corebetween the opposed terminals of the two groups to thus each form asingle turn secondary winding.

The embodiment of FIG. 1 as assembled is depicted in an end view in FIG.2 illustrated to a slightly reduced scale. Accordingly, the elements inFIG. 2 are identified by the same numerals used in connection with theillustration of FIG. 1. There is visible in this view circuit board 3,the transformer coil 5, cable 21 with the left end connector 23 and theright end connector 25 engaged in the terminals, the latter of which arenot visible in this view. As is clearly illustrated, cable 21 windsaround the underside of the coil 5 and extends through the core so as toform a loop or arc, as variously termed, which extends around the coilover a distance of more than 180 degrees (π radians) and though in theliteral sense is less than a complete turn of 360 degrees, eachconductor of the cable is effectively a one-turn or single turntransformer winding. Moreover, the cable 21 is seen to serve as a strapin that it folds over and around each of the outer core legs, therebyrestraining movement of the transformer away from the circuit board. Itis understood, however, that the restraint or support provided by thiscable or winding for the transformer on the circuit board may by itselfbe sufficient to hold the transformer in place. However, it isrecognized that other electrical connections may be made between thetransformer windings and the circuit board which will serve to provideadditional support. The advantage, either separately or in combinationwith additional restraints, is that the transformer may be held in placewithout the necessity for screws, bolts, and brackets. By way of furtherimprovement upon this support function, reference may be made to FIG. 3in which I depict in an end view schematically the assembly 3 which maybe representative of a completed circuit board containing aninverter-oscillator type arrangement for operating one or morefluorescent type lamps which is normally placed in a container 30 havinga lid 32 and having one container "potted" or encased in a knownelectrically insulative heat conductive potting compound 33, asrepresented in the figure. Those types of thermal setting orthermoplastic type potting compounds are well known in this kind ofapplication, such as asphalt, which are inserted in a liquid state andafter curing either by standing or by heating form a solid body andadhere to the walls of the container as well. This potting materialserves to encase and hold in place transformer 1 very securely and inthis sense the strap serves a temporary support function prior to thetime the entire unit, including the transformer and circuit board, isencased in the epoxy. The arrangement avoids need for screws and boltsto provide such a temporary fastening.

The transformer of FIG. 1 may be represented by an electrical schematicdepicted in FIG. 4, in which the core is represented by the threeparallel lines, the primary winding 8' containing the leads 7', 9' and11', the high voltage secondary 10 containing the leads 13', 15' and17', referred to in the figure, as well as the plurality of single turnwindings 21' formed by cable 21 and the single "two-turn" winding formedby two of the leads in the cable in combination with the conductor onthe circuit board, represented by a dash line bridging conductor 28' inthis schematic. As in all transformers, each of the windings are"electromagnetically" coupled to another and to the core of magneticmaterial.

Given the preceding description of the electrical and mechanicalstructure of the preferred embodiment of my invention, the alternateembodiments are easily understood and variations on all of thestructures suggest themselves to the skilled reader. For convenience,similar parts used in the alternate embodiments are identified by thesame numbers as corresponding elements earlier presented anddistinguished by the addition of a single or double prime in conjunctionwith the number.

As represented in FIG. 5, a transformer having an E-I type magnetic core1' is shown in end perspective view and contains coil 5' comprised of aprimary and a secondary winding, each containing a large number of turnsof enamel insulated wire, and a cable 21', with the entire assemblysupported upon circuit board 3'. In this embodiment, the ends of thecable do not include the cable connectors shown in the earlierembodiment but the cable ends are stripped of insulation and the exposedconductors are inserted directly into the corresponding terminalopenings located in circuit board 3' and are soldered in place. Cable21' extends in a loop about the outer periphery of coil 5', over anarcuate length of at least 180 degrees around the axis of the coil, withthe ends of the cable extending through the clearance space between eachof the outer core legs and the peripheral surface of coil 5'. As in theearlier described embodiment, cable 21' forms a straplike restraintholding the transformer to the board with the assistance of the solderwhich forms the electrical and mechanical coupling between the cableends and the circuit board.

As is apparent, the loop formed by the cable extends at least 180degrees but less than 360 degrees arcuate distance about the peripheryof coil 5'. It is clear that the embodiments of FIGS. 4 and 5 may bemodified to include cable connectors, such as connectors 23 and 25 ofFIG. 1. Likewise, rather than directly plugging these connectorsdirectly into the circuit board, corresponding mating connectors may bemounted to the circuit board to which the cable connected connectors maybe coupled to form an electrical and mechanical juncture. I prefer anyparticular structure which satisfied good practices and is satisfactoryfor any particular application at the lowest possible cost.

Briefly, making reference again to the embodiment of FIG. 1, I thereillustrate the structure by means of which a plurality of voltagestep-down secondary windings, each of a single turn, are formed simplyby looping or placing a flat multiconductor cable around the peripheryof a mounted coil, including the axially extending core portion, over anarcuate distance about that axis of at least 180 degrees, as well as thestructure for providing a coil of two turns by using at least two of theparallel extending conductors in the cable in conjunction with a printedconductor 28 located on the surface of circuit board 3, which printedconductor extends between one terminal in the right hand group ofterminals 27 to another terminal in the left hand group of terminals 29.Considering the terminals in group 27 as A, B, C, D, E and F, from frontto back, with A the closest to the viewer, and corresponding terminalsin terminal group 29 similarly characterized, the electrical path isdefined from terminal A of group 29 through the corresponding conductorin cable 21 around the periphery of the coil to terminal A in terminalgroup 27, then over conductor 28 across the surface of the board toterminal B in group 29 and from there through the next conductor incable 21 again around the periphery of coil 5 and the center leg, overto terminal B in group 27. In effect, the electrical path goes aroundthe magnetic core twice as is equivalent to a two-turn coil.

Other terminal arrangements and conductor arrangements are evident fromthe foregoing description of the structure of my invention and forillustrative purposes I present examples in FIGS. 6 and 7. In FIG. 6 theelectrical conductors within the cable 21, not illustrated in thisfigure, is represented in dash lines and extend between terminals incircuit board defining the right hand group of terminals 27', and theleft hand group of terminals 29' on circuit board 3a, partiallyillustrated. In this alternative, a double turn coil is formed byconductor 28' extending between the A terminal of group 27' to the Eterminal of group 29' with the ends of the two-turn coil appearing at Dterminal of group 27' and A terminal of group 29'. As is apparent fromthe electrical path indicated by the arrows, including those definedthrough space conductors in the cable, in this variation the two-turncoil is formed using two of the cable conductors which are spaced fromone another by two other cable conductors and not adjacent cableconductors as was the case in the embodiment of FIG. 1. There is thus norequirement for the adjacent cable conductors to be used to form amultiturn winding. To add turns to a coil, one simply ensures that theturns in the cable conductor are properly oriented so that the currentpath always passes in the same direction about the transformer core sothat the individual voltages induced in each portion of each turn in thecoil combine electrically in an additive manner.

By way of further illustration, a three-turn coil winding arrangementusing the aforedescribed cable and circuit board conductor arrangementis illustrated, and in which the circuit board 3b and correspondingterminal groups are identified by the same numerals but double primed.Thus the circuit board 3b in the embodiment of FIG. 7 includes twospaced conductors 28" extending between the A terminal of group 27" andthe B terminal of group 29" and additionally a second, essentiallyparallel conductor, 26', extending between the B terminal of group 27'to the C terminal of group 29'. Additionally, the cable conductors ofthe cable, not illustrated in this figure, are represented as dash linesextending in a loop between opposed terminals in each group. In thethree-turn coil defined, a current path is represented by the arrowsextending from the A terminal of group 29" through the cable conductorto the corresponding A terminal of the other group, thence overconductor 28" on the circuit board to the B terminal of group 29", andfrom that B terminal through the next cable conductor over to the Bterminal of group 27", and over the circuit board conductor 26" to the Cterminal of group 29 through the third cable conductor to the C terminalof group 27". As represented by the arrows, the electrical current pathgoes through the cable and around the magnetic core three times in thesame direction and hence is effectively a three-turn electrical coil.The connection arrangement of FIG. 7 thus shows a three-turn windingformed between the cable and the conductors on the circuit board inaddition to three one-turn secondary windings.

An addition embodiment of the transformer invention is illustrated inFIG. 8 in which, for convenience, the elements previously illustrated inconnection with earlier embodiments and corresponding thereto areidentified by the corresponding numeral and a differnet alphabeticcharacter. Thus as depicted in an end view in FIG. 8, core 1_(c) isformed of the E and I magnetic laminations aranged in a conventionalstructure and an electrical coil 5_(c) mounted to the center core leg.Coil 5_(c) contains a multi-turn primary winding and an overlyingmulti-turn secondary winding, which in connection with the previousembodiments and one specific example thereof included a ninety turnprimary and three single windings and one two-turn winding overlying thesecondary. The coil and core structure is situated on top of a printedcircuit board 3_(c). The ribbon-like cable 21c is formed into a loop,which loop extends about the axis of the right outer core leg of thecore, which core leg appears on the righ-hand side of the figure. Oneportion of the cable extends through the space in the core "window"between the outer leg and peripheral surface of coil 5_(c) downwardly toan end connection to printed circuit board 3_(c) ; the other cableportion extends about the outside of the right core leg to a connectionon circuit board 3_(c) spaced from the other cable end. As is apparent,the cable forms a loop extending approximately at least 180 degreesabout the axis of the right core leg. As in the previously describedembodiments of the invention, cable 21_(c) is of a ribbon-like geometrycontaining at least three and as many as twenty spaced parallelinsulated electrical conductors. In the defined structure each of suchcable conductors forms a fractional turn secondary winding, morespecifically, a one-half turn winding because, as is understood by thoseskilled in the art, each cable conductor extends through the core windowonly once. By contrast, in the previous embodiments of FIGS. 1, 2 and 5the cable extended through the core "windows" twice so that each cableconductor forms one turn or a single-turn secondary winding. As wasdescribed previously in connection with FIG. 1 and in the alternativeconnections of FIG. 6 and FIG. 7, various connecting terminals andprinted circuit wiring may be included on a surface of circuit board3_(c), by means of which one or more of the spaced conductors may beconnected to other electrical components not illustrated, or one or moreof the cable conductors may be interconnected or linked to form amultiple-turn winding that is some multiple number of one-half turns.And as is apparent, some of the electrical conductors in the cable neednot be utilized for practical reasons. For example, assuming a standardribbon cable can be purchased and contains ten conductors and in apractical embodiment only eight of the conductors are required. It ismore cost effective to purchase the standard cable and to use only asmany conductors, such as eight, as is needed, leaving the remaining twounutilized, than to purchase a nonstandard cable containing only theprecise number of conductors, which is likely to cost substantially morethan the standard cable. As in the preceding embodiments, the loopformed of cable 21_(c) forms a strap-like arrangement which partiallyholds the core 1_(c) and coil 5_(c) upon the circuit board 3c,satisfying a mechanical function.

A variation of the embodiment presented in FIG. 8 is illustrated in FIG.9 where similar elements are identified by the same numerals but with adifferentiating alphabetic letter. In this embodiment, a first cable21_(d) is looped about the right hand outer core leg and has its endsconnected electrically and mechanically to circuit board 3_(d) as in theembodiment of FIG. 8. In addition, another ribbon-like flatmulticonductor cable 22_(d), which may be substantially identical to ordifferent from cable 21_(d), contains a portion looped about the leftouter core leg lamination and the ends thereof downwardly depend forconnection to circuit board 3_(d). As is apparent, the cable 22_(d)extends through the core window only once. Thus each conductor in thecable forms effectively a one-half turn secondary winding. As in theprior embodiments, the ends of the electrical conductors contained incable 22_(d) may be connected in circuit with separate electricalcomponents, and may be interconnected to form a secondary winding whichconsists of some multiple of one-half turn, either or both of which areaccomplished by means of electrical conductors printed on circuit board3_(d). Additionally, the windings formed by the conductors in each ofcables 22_(d) and 21_(d) may be suitably interconnected in series aidingor in series opposition by suitable electrical conductors printed uponthe circuit board 3_(d), much in the manner described in connection withFIGS. 6 and 7 of the prior embodiments. Many obvious variations of thedisclosed electrical interconnections come within the scope of thedisclosed invention, all of which become apparent to the skilledtransformer designer upon reading this specification and which, in theinterest of conciseness, need not be illustrated or described to theinfinite degree possible. As is also apparent from the end view of theembodiment of FIG. 9, cables 21_(d) and 22_(d) serve as fastening strapsrestraining opposite outer core legs of core 1_(d) providing amechanical restraint holding core 1_(d) and coil 5_(d) upon circuitboard 3_(d).

FIG. 10 depicts still another embodiment of the inventiondistinguishable from the embodiment of FIG. 8 in that the core 1_(e) ismounted in an up-ended position having the outer core leg restingagainst the upper surface of the printed circuit board 3_(e), the latterof which serves as the support for the assembly of core 1_(e) and coil5_(e). As shown in this end view, the ribbon-like multiconductor cable21_(e) is looped about the outer core leg by at least 180 degrees andthe cable ends are attached to the circuit board. As in the embodimentof FIG. 8 the cable 21_(e) forms a loop which extends once through thecore "window" and hence each conductor in cable 21_(e) forms afractional, more specifically, a one-half turn secondary. And thewinding serves also to strap the core and coil to the circuit board.

An additional embodiment presented in FIG. 11 includes the core 1_(h),the coil 5_(h), and the strap cable 21_(h), mounted to the circuit board3_(h), with the electrical leads formed at the end of cable 21mechanically and electrically connected to the board by the solder 12and 14. In this embodiment the core 1_(h) is upright with an outer coreleg located in contact with the circuit board. The transformer is heldagainst the surface of circuit board 3_(h) by the strap-like restraintof cable 21_(h). The cable extends in a loop about the axis of coil5_(h) and the outer periphery of the coil, as well as about the axis ofthe center core leg on which coil 5_(h) is mounted, with the strapextending through the clearance between the periphery of coil 5_(h) andthe outer core leg located at the topside of the figure.

A still further embodiment is illustrated in end view in FIG. 12. Thecoil 5_(f) and the core 1_(f) containing the coil is shown in end viewseated upon the printed circuit board 3_(f) which can be considered thesame in structure as those corresponding elements of the embodiment ofFIG. 8. The multiconductor ribbon-like cable 21_(f) is formed into awide loop which extends around the periphery of the axis of coil 5_(f)as well as the left side core leg by at least 180 degrees; one dependingend length portion of the cable extends through one core window inbetween the periphery of coil 5_(f) and the inner surfaces of the righthand side outer core leg 1_(f) to the circuit board and the otherdepending end length portion of the cable extends around the outersurface of the left hand outer core leg and therefrom down to connectionwith circuit board 3_(f). In this embodiment, a greater length of cable21_(f) is employed in comparison to that used in the embodiment of FIG.8 given the same core size. The ribbon-like cable extends much like awide strap about the core and coil to provide a better mechanicalrestraint or strap temporarily fastening the core and coil 5_(f) to theboard more firmly than in the case of the embodiment of FIG. 8. Theplural conductors in cable 21_(f) may be interconnected as desired inthe manner described in connection with the preceding embodiments toform either a plurality of secondary windings or at least one secondarywinding that is some multiple of a one-half turn.

An additional embodiment combines the structure of the single-turnwindings presented in the embodiment of FIG. 5 and the structure of thehalf-turn secondary windings presented in the embodiments of FIGS. 8through 12 is presented in FIG. 13. Thus, as in the previousembodiments, the magnetic core 1_(g) formed of standard E and Ilaminations with a center and two outer core legs, defining two corewindows, supports the coil 5_(g) axially mounted upon the center coreleg and containing the multiturn primary winding and the overlyingmultiturn secondary winding, which are of conventional coil structureknown to those skilled in the art, and the core rests upon the surfaceof a circuit board 3_(g) as in the embodiments previously described.Multiconductor cable 21_(g) is formed into a loop which, as depicted,extends over the periphery of coil 5_(g) and twice through the corewindow in between the outer core legs extending about the axis of thecoil by at least 180 degrees and has its ends attached to the circuitboard corresponding to the embodiment of FIG. 5. Thus each conductor incable 21_(g) forms a single-turn secondary winding. These individualwindings may be separately connected to separate conductors on the boardor some of these windings may be electrically interconnected in themanner previously described for the earlier embodiments to placeindividual windings in series or parallel, particular attention beinggiven to FIGS. 1, 6 and 7 for the connections. A second ribbon-likecable 22_(g) is formed into a loop which extends about the axis of theright-hand outer core leg by at least 180 degrees with one end of thecable extending through a core window. The ends of cable 22_(g) areconnected to spaced terminals on circuit board 3_(g). As in the case ofthe embodiments of FIGS. 9 through 12, each of the electrical conductorsin cable 22_(g) forms a fractional one-half turn secondary winding, andthese may be separately connected to other electrical components orwiring on the circuit board not illustrated in the manner previouslydescribed, or have adjacent or various conductors within the cableinterconnected by means of printed circuit wiring on top of the circuitboard to form secondary windings of some multiple of a one-half turnwinding. Additionally or alternatively, one or more windings on cable22_(g) is interconnected with at least one of the conductors in thecable 21_(g).

Although I have illustrated the structure of my novel method andapparatus employing a flat cable containing six parallelly extendingelectrically insulated electrical conductors, it is apparent that othernumbers of conductors may be used depending on the requirements of anyspecific circuit and the number of turns in the winding desired. Thuswhile six is illustrated, seven or more may be incorporated in whichcase corresponding terminals may be fabricated on the circuit board forsuch specific application.

The simultaneous addition of the single turn windings by the cable 21 inthe embodiment of FIG. 1 may be manufactured according to one specificmethod by fabricating the core 1 and coil configuration 5 byconventional methods which usually involves winding coil 5, mounting thecoil on the center E-shaped transformer portion and then adding the Ilamination in place to clamp the coil 5 in place on the magnetic core.By taking the cable with the bare ends and looping it around the coil 5and threading it through the clearance openings on either side of thecoil between the coil and the outer coil legs, the connectors 23 and 25may be added thereafter. Alternatively, a cable of the desired lengthprefabricated to include connectors 25 and 23 may be similarly threadedthrough the clearance between the outer core legs and looped around thecoil over at least 180 degrees arcuate distance providing there issufficient clearance between the coil and outer core legs with which toallow the connectors to be threaded through.

A still alternative manner, for example with or without connectors, isafter manufacture of the coil 5 simply to loop the cable about the coilaxis and insert both coil 5 and the flat cable simultaneously onto the Ecore prior to adding the I portion, which is thereafter accomplished. Ineach of the foregoing methods, the additional transformer windings areformed by looping or wrapping the flexible multiconductor cable aboutthe periphery and axis of the generally cylindrical or rectangular typecoil formed of enamel coated wire and containing the primary winding.The same methods of construction may be used to produce the structure ofeach of the other embodiments.

It is believed that the foregoing description of the preferredembodiments of my transformer apparatus and my method of adding windingsis presented in detail sufficient to enable one skilled in the art tomake and use the invention as well as to practice the method withoutundue experimentation. I do not intend however that the detailspresented for the foregoing purpose be construed to limit my invention,inasmuch as various equivalents and modifications thereto which becomeapparent to those skilled in the art upon reading this specification maybe made, all of which contain my invention as herein disclosed.Accordingly, it is respectfully requested that my invention be broadlyconstrued within the full spirit and scope of the appended claims.

What I claim is:
 1. The electrical apparatus which comprises incombination:a metal container means having an opening and a lid forclosing said opening; a printed circuit board of electrically insulativebase material containing a plurality of flat electrical conductors on atleast one surface thereof; a first set of spaced electrical terminalsand a second set of spaced electrical terminals; a core of magneticmaterial forming a magnetic circuit, said core including a center coreleg and first and second outer core legs located on opposite sides ofsaid center leg and extending parallel thereto to define therebetween acoil-receiving window; electrical coil means having an axially extendingcentral passage comprising a first primary winding containing a firstmultiple number of turns of enamel insulated electrical wire and atleast one secondary winding comprising a second multiple number ofturns, greater than said first multiple number, of enamel covered wirewith said first winding overlying said second winding and said coilincluding an axially extending passage, said electrical coil means beingmounted along the axis thereof on said center core leg with a clearancespace between the outer periphery thereof and each of said outer corelegs; an elongate relatively flat cable means having a widthsubstantially greater than the thickness thereof and containing at leastthree spaced parallel conductors extending between a first and secondend of said cable means in electrical insulated relationship with oneanother; said cable means extending in a loop about the periphery ofsaid electrical coil means and over an arcuate distance therearound ofgreater than 180 degrees but less than 360 degrees and extending throughthe clearance space between said periphery of said coil means and atleast one of said outer core legs; means electrically and mechanicallycoupling said first end of said cable means to corresponding terminalsin said first set of electrical terminal means on said printed circuitboard; and means electrically and mechanically coupling the conductorsat said second end of said cable to corresponding ones of saidelectrical terminals in said second set of electrical terminal means;and wherein each of said core, coil means, cable and printed circuitboard being disposed within said container means with said core andelectrical coil means supported on a surface of said printed circuitboard; a plurality of electrical components mounted on said circuitboard in an electrical circuit, and means, including said plurality offlat electrical conductors on said circuit board, adapted toelectrically interconnect said electrical components in circuit witheach of said primary and secondary winding of said coil means, and saidfirst and second set of electrical terminal means; and electricallyinsulative potting material disposed within said container for encasingsaid circuit board, core, coil means, cable and electrical componentstherewithin.
 2. The invention as defined in claim 1 wherein each of saidfirst and second means for connecting said first and second cable endsto said respective first and second set of terminal means each compriseelectrical connector means.
 3. The invention as defined in claims 1 or 2wherein said printed circuit board includes at least one electricalconductor extending between one terminal means of said first set ofelectrical terminals and one terminal means of said second set ofelectrical terminals.
 4. The electrical apparatus which comprises incombination:a printed circuit board of electrically insulative basematerial containing a plurality of electrical conductors on at least onesurface thereof; a first set of spaced electrical terminals and a secondset of spaced electrical terminals; a core of magnetic material forminga magnetic circuit, said core including a center core leg and first andsecond outer core legs located on opposite sides of said center leg andaxially extending parallel thereto to define therebetween acoil-receiving window; electrical coil means having an axially extendingcentral passage comprising a first primary winding containing a firstmultiple number of turns of enamel insulated electrical wire and atleast one secondary winding comprising a second multiple number of turnsof enamel covered wire with said first winding overlying said secondwinding, said electrical coil means being mounted along the axis thereofon said center core leg with a clearance space between the outerperiphery thereof and each of said outer core legs; an elongaterelatively flat cable containing a plurality of spaced parallelconductors extending between a first and second end of said cable inelectrical insulated relationship with one another; said cable extendingin a loop about the axis of one of said outer core legs over an arcuatedistance between approximately 180 degrees and less than 360 degrees andextending through the clearance space between said periphery of saidcoil and said one outer core leg; means electrically and mechanicallycoupling said first end of said cable to corresponding terminals in saidfirst set of electrical terminal means on said printed circuit board;and means electrically and mechanically coupling the conductors at saidsecond end of said cable to corresponding ones of said electricalterminals in said second set of electrical terminal means; a pluralityof electrical components mounted on said circuit board in an electricalcircuit; and means, including said plurality of flat electricalconductors on said circuit board, adapted to electrically interconnectsaid electrical components in circuit with each of said primary andsecondary winding of said coil, and said first and second set ofelectrical terminal means.
 5. The apparatus of claim 4 wherein the cableend extending through the clearance space further extends around theouter periphery of the coil over an arcuate distance of betweenapproximately 180 degrees and less than 360 degrees, passes through theclearance space between the other outer core leg and the periphery ofthe coil means and extends about the axis of the other center core leg.6. The apparatus of claim 5 wherein the core is oriented with respect tothe printed circuit board so that the cable passes along the undersideof the coil extends upward through the clearance spaces and over each ofthe outer core legs.
 7. The electrical apparatus which comprises incombination:a printed circuit board of electrically insulative basematerial containing a plurality of flat electrical conductors on atleast one surface thereof; a first set of spaced electrical terminalsand a second set of spaced electrical terminals; a core of magneticmaterial forming a magnetic circuit, said core including a center coreleg and first and second outer core legs located on opposite sides ofsaid center leg and axially extending parallel thereto to definetherebetween a coil-receiving window; electrical coil means having anaxially extending central passage comprising a first primary windingcontaining a first multiple number of turns of enamel insulatedelectrical wire and at least one secondary winding comprising a secondmultiple number of turns, greater than said first multiple number, ofenamel covered wire with said first winding overlying said secondwinding and said coil including an axially extending passage, saidelectrical coil means being mounted along the axis thereof on saidcenter core leg with a clearance space between the outer peripherythereof and each of said outer core legs; an elongate relatively flatcable containing a plurality of spaced parallel conductors extendingbetween a first and second end of said cable in electrical insulatedrelationship with one another; said cable extending in a loop about theperiphery of said electrical coil means and over an arcuate distancetherearound of greater than 180 degrees but less than 360 degrees andextending through the clearance space between said periphery of saidcoil means and at least one of said outer core legs; means electricallyand mechanically coupling said first end of said cable means tocorresponding terminals in said first set of electrical terminal meanson said printed circuit board; and means electrically and mechanicallycoupling the conductors at said second end of said cable tocorresponding ones of said electrical terminals in said second set ofelectrical terminal means; a plurality of electrical components mountedon said circuit board in an electrical circuit, and means, adapted toelectrically interconnect said electrical components in circuit witheach of said primary and secondary winding of said coil means, and saidfirst and second set of electrical terminal means.
 8. For use with anelectrical transformer of the type including:a core of magnetic materialincluding a center core leg and first and second outer core legs, andprimary and secondary windings mounted about the core and respectivelyincluding a first and a second multiple number of turns of insulatedelectrically conductive wire, the primary winding being mounted aroundthe center core leg, a method for adding a plurality of low voltageelectrical windings comprising the step of: looping a flat cablecontaining a plurality of spaced parallely extending insulatedelectrical conductors about the peripheral surface of the primarywinding through an arcuate distance in the range of approximately 180degrees to less than 360 degrees.
 9. For use with an electricaltransformer of the type including:a core of magnetic material includinga center core leg and first and second outer core legs, primary andsecondary windings mounted about the core and respectively including afirst and a second multiple number of turns of insulated electricallyconductive wire, the primary winding being mounted around the centercore leg, a method for adding a plurality of fractional turn windingscomprising the step of: looping a flat cable containing a plurality ofspaced parallely extending insulated electrical .[.conducts.]..Iadd.conductors .Iaddend.about one of the outer core legs through anarcuate distance in the range of approximately 180 degrees to less than360 degrees.
 10. For use with a printed circuit board having a pluralityof terminal members adapted to receive and secure the leads extendingfrom electrical components, and an electrical transformer of the typeincluding:a core of magnetic material including a center core leg andfirst and second outer core legs, on opposite sides of the center coreleg at least a portion of each outer leg extending generally parallel tothe center core leg, primary and secondary windings mounted about thecore and respectively including a first and a second multiple number ofturns of insulated electrically conductive wire, the primary windingbeing mounted around the center core leg, a method comprising the stepsof: looping a flat cable containing a plurality of spaced parallelyextending insulated electrical conductors under the lower peripheralsurface of the primary winding so that the cable passes between thewinding periphery and the outer core legs; folding the opposite ends ofthe cable over the respective outer core legs; and securing theconductors at each cable end to respective terminals on the printedcircuit board to form a number of additional single-turn windings aboutthe core while simultaneously securing the transformer to the printedcircuit board.
 11. An improved electrical transformer of the typeincluding:a core of magnetic material including a center core leg andfirst and second outer core legs, and primary and secondary windingsmounted about the core and respectively including a first and a secondmultiple number of turns of insulated electrical conductors, the primarywinding being mounted around the center core leg, wherein theimprovement comprises: a relatively flat multi-conductor cable extendingin a loop about one of the outer core legs over an arcuate distance ofapproximately 180 degrees to less than 360 degrees; the ends of theconductors being adapted for electrical coupling external of thetransformer to function as a plurality of fractional-turn windings. 12.The transformer as defined in claim 11 wherein said plurality ofconductor in said flat cable is the number six.
 13. The transformer ofclaim 11 wherein the cable further extends about the periphery of theprimary winding over an arcuate distance of approximately 180 degrees toless than 360 degrees and thereafter extends in a loop about the otherouter core leg over an arcuate distance of approximately 180 degrees toless than 360 degrees whereby the electrical coupling of the cable endsto electrical components additionally secures the transformer.
 14. Theinvention as defined in claim 13 further comprising in combination:aflat printed circuit board; and means securing said first and secondcable ends to first and second locations on said printed circuit boardto couple said electrical transformer to said circuit board. .Iadd. 15.For use with an electrical transformer of the type including electricalcoil means containing a primary winding and at least one secondarywinding, said coil means having a central axis and a central passageco-axial with said axis; a core of magnetic material extending throughthe central passage to mount the coil about the core,a method for addinga plurality of fractional turn windings comprising the step of looping aflat cable containing a plurality of spaced parallely extendinginsulated electrical conductors about the coil means so that it curvesthrough an arcuate distance in the range of approximately 180 degrees toless than 360 degrees. .Iaddend.